Recently, with a progress in micro processing techniques, it becomes possible to form a concave-convex microstructure of nano scale on a surface of an article. The concave-convex microstructure of nano scale exhibits a structure-derived function such as an antireflection function referred to as a moth-eye effect or a water repellant function referred to as a lotus effect. Therefore, the industrial use of the concave-convex microstructure of nano scale (improvement in light extraction efficiency of organic EL elements, antireflection of image display apparatuses, improvement in image clarity of image display apparatuses, water repellant materials for various members, or the like) is actively made.
As a method of forming a concave-convex microstructure on a surface of an article, for example, the following method is known:
a method of transferring a concave-convex microstructure on a surface of an article by using a cylindrical nanoimprinting mold in which an oxide film (anodic porous alumina) having a plurality of fine pores is formed on an outer peripheral surface of a cylindrical aluminum substrate.
The method is suitable for industrial production since the concave-convex microstructure can be formed on the surface of the article with few simple steps.
Further, as a method of forming an oxide film having a plurality of fine pores on a surface of an aluminum substrate, for example, the following method is known:
a method of anodizing a surface of an aluminum substrate after the surface of the aluminum substrate is polished (Patent Document 1).
When the surface of the aluminum substrate is polished before anodization is performed and the surface roughness is decreased to be uniform until the surface becomes a mirror surface, occurrence of unevenness in the oxide film can be suppressed. As a result, it is possible to form a concave-convex microstructure with higher accuracy on an article.